An analysis of the speeches given by party leaders at their annual conferences has revealed a marked increase in religious language since 2001.

Between 1998 and 2007, Prime Minister Gordon Brown used religious references most on average, with just one speech, according to a report from church-backed theology think tank Theos.

At the 2007 conference, when he famously referred to “the sermons my father preached Sunday after Sunday,” Mr Brown made 14 religious references in his first speech as party leader, compared with Tony Blair’s average of 9.3 and David Cameron’s 8.3.

Brown, Blair, Cameron and Iain Duncan-Smith seemed more comfortable with references to God with more than eight references per speech,

William Hague, Ming Campbell, Charles Kennedy, Michael Howard and Paddy Ashdown each made fewer than five per speech.

“In contrast to a comparative analysis of US presidential speeches, the use of religious rhetoric by UK political leaders is notably more subtle and indirect,” reports Theos.

“In the UK, leaders often talk about faith but ‘God’ is referred to directly only 7 times in the 30 speeches analysed. In comparison, George W. Bush invoked God in 94% of presidential addresses through the first six years of his presidency.”

Commenting on the findings of the research, the Director of Theos, Paul Woolley, said:

“The increase in references to religious faith reflects an increased awareness of, and interest in, religious groups in our society.

“Faith groups represent a growing constituency in society and are often at the forefront of community activism. They are frequently the first in and last out in some of our most deprived communities.

“In some respects, politicians cannot afford not to do God.

“Talking God is not the same as ‘doing God’.

“It is entirely right that politicians should draw on religion to shape and inspire their rhetoric, but that is no substitute for what the Christian tradition sees as good leadership – governing with justice and mercy.”

There is a spike in 2001, reports Theos, when each of the speeches was delivered within a few weeks of the 9/11 attacks.

In 2001, the three leaders between them made over 50 religious references, Blair making 32 compared with Duncan-Smith’s 16, and Charles Kennedy’s five.

Prior to 2001 (i.e. 1998-2000) there are, on average, 11 references and allusions made in party conference speeches per year, whereas after 2001 there are more than 16.5.

The report should please Roman Catholic leaders, who have accused both Tony Blair and Gordon Brown of ignoring religious opinion.

In November 2007 Cardinal Murphy-O’Connor criticised the Human Fertilisation and Embryology Bill , saying that it is “profoundly wrong” to allow lesbian couples to conceive children.

Earlier that year he became the first Catholic leader in nearly 200 years to question whether the policy of the government is at odds with practising the Roman faith.

He accused the British government of creating, “a different version of our democracy, one in which diversity and equality are held to be at odds with religion.”

In a lecture in London, the Cardinal said that Roman Catholics and other Christians and faith groups were going to demand their rights to continue to discriminate against gay couples when providing adoption services.

Scots bishops went further in directly attacking the Labour leadership over its support for the Human Fertilisation and Embryology Bill.

Bishop Jim Devine’s attacked as the Glasgow East constituency was in the middle of a by-election that Labour lost.

“Christian people have not changed. It is Labour that has broken its pack with Christian voters,” he wrote in a letter to all MPs representing Scottish constituencies.

“What are we to do when our religion is attacked and our conscience outraged?

“When one considers the self-inflicted injuries this Labour Government has visited upon itself, one could be forgiven for thinking it had some kind of death wish.”

Tony Blair converted to Catholicism months after leaving office last year.

Mr Blair’s relationship with the gay community was seriously damaged following his appointment of the devoutly Catholic Ruth Kelly to the post of Minister for Equality in 2006. Ms Kelly, a member of Opus Dei had never voted in favour of gay rights despite her role holding responsibility for LGBT issues.

When Mr Blair was tempted to side with Ms Kelly and Roman Catholic adoption agencies over an exemption to the sexual orientation regulations, Peter Hain and Alan Johnson threatened to quit the cabinet.

The conversion comes after years of speculation that Mr Blair, whose wife Cherie and four children are Catholic, would convert from Anglicanism after he left office.

One of his final acts as prime minister was to visit Pope Benedict in June – his third Vatican trip in four years.